Reduction of sludge deposition from crude oils



Aug. 30, 1960 J. O'DONNELL ETAL 7 2,951,037

REDUCTION OF SLUDGE DEPOSITION FROM CRUDE OILS Filed Dec. 20, 1954 3 Sheets-Sheet l FIELD 9 L lzgil. O

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Aug. 30, 1960 J. O'DONNELL ETAL 2,951,037 I REDUCTION OF swocr: DEPOSITION FROM CRUDE OILS Filed Dec. 20. 1954 s sheets-Shea;

1 Psnceunee 0F TOTAL SLUDGE nEPosiTEb FIELD! I I 1a m a PERCENTAGE or TOTAL SAMPLE nzwosrrsn I a PERCENTAGE or TOTAL SAMPLE nswosmzo HEAT TREATMENT cum A 2l2-60F GuRvE a 2\2-60'-100-60F 5 B C 2'0 4'0 6'0 do 2'0 4'0 60 5'0 HouRs SETTLING m A are COLUMN HOURS BETTLING IN A 3Foo-r COLUMN 15 1.4 A 1 L7 u Y I-5W 6/ 1 United States Patent REDUCTION OF SLUDGE DEPOSITION FROM CRUDE OILS James ODonnell and Donald Frederick Duckworth,-.i mbury-on-Thames, England, assignors to The British Petroleum Company Limited This invention relates to a process for reducing the sludge forming tendencies of crude oils.

It is well known that on storage certain crude oils of parafiinic or parafiinic-asphaltic type deposit a wax-containing sludge which represents a loss of material and which means that tanks on land or on board ships have to be cleaned out from time to time. I

We have now developed a process for treating such crude oils which results in a considerable reduction in the sludge deposition fro-m the oils on subsequent storage.

The invention consists in heating the crude oil from a temperature below 100 F. and preferably not higher than 70 F., to an elevated temperature as hereinafter defined. 1

By elevated temperature we mean temperature within a range which is characterized by the fact that if the crude oil is heated from a temperature below 100" F. or, better, still, not higher than 70 F. to a temperature within that range and then cooled, considerably less sludge is deposited from the crude oil on subsequent storage than would have been deposited if the crude oil had not been so heated. The temperature range varies with the source of the crude oil and it may easily be determined, for any particular crude oil, by a simple test to be described shortly. The duration of the heating step is not important so far as now appears since the same results were obtained when a sample of oil was heated to the appropriate elevated temperature for one minute as when another sample of oil from the same source was heated to the same temperature for 48 hours.

In the case of crude oil coming directly from an oil Well, it must first of all be cooled to a temperature preferably not higher than 70 F. and then heated to the elevated temperature. The precooling may be done after the oil issuing from the well has been passed to a separator or stabilizer but where there is no stabilizer and the crude oil is degassed entirely in separators the cooler may be placed before the separator unit.

Of the drawings:

Fig. 1 is a graph of curves illustrating the effect on sludge deposition of precooling at various temperatures, in the case of two crude oils from two different Middle Eastern fields;

Fig. 2 is a graph illustrating the relationship of the optimum heat treatment temperature for minimum sludge deposition to the temperature at which the crude oil is stored (reservoir temperature), in the case of crude oils from various Middle Eastern fields;

Fig. 3(a) is a graph of curves illustrating the eifect on the sludge settling rate of heat treating after precooling, at the optimum heat treatment temperature, in the case of samples of a typical Middle Eastern crude oil;

Fig. 3(b) is a graph illustrating the effect on the sludge settling rate, of heat treating, after pre-cooling, at the optimum heat treatment temperature (curve B) and at a lower temperature (curve C), in the case of samples of a typical Middle Eastern crude oil;

2,951,037 Patented Aug. 30, 1960 Figs. 3(0) and 3(d) are graphs comparable to Figs. 3(a) and 3(b), respectively, but illustrating the eifectof the heat treatment on both the settling rate and the amount of waxy material in the crude oil available for deposition; and,

Fig. 4 is a flow diagram schematially illustrating one mode of applying the process to crude oil coming directly from a well.

The advantage of precooling well head crude oil to 70 F. or lower before heating to the elevated temperature are shown in Figure 1 of the accompanying drawings, which illustrates the results obtained when crude oil from two Middle Eastern fields is subjected to various degrees of precooling. I

The process may also be used at a refinery in which case the crude oil, if it has already cooled in transit to a temperature of 70 F. or lower, may be heated directly to the elevated temperature and then cooled for storage and processing.

The elevated temperature or elevated temperature range above referred to may be determined by the following test. A sample of the crude oil is heated in a pressure tight bomb to 212 F. and is maintained at this temperature for one hour. It is then cooled to 60 F. (If the sample has been freshly taken from a well separator or stabiliser the heating step can be omitted since its purpose is merely to eliminate any previous thermal history of the sample.) The sample (at 60 F.) is then divided into a number of portions which are heated for one hour to various temperatures Within .the range of 60 F. to 212 F. preferably at narrow intervals say of 15 F. The portions are then cooled to 60 F. and after standing for 12 hours are centrifuged for 15 minutes (using a machine capable of giving a force of 1000 G). It will be found that a minimum sludge deposit will result in portions which have been heated to a certain temperature or temperatures and further portions of the sample may then be heated to temperatures at narrow intervals around this temperature or these temperatures in order to find more accurately the temperature range corresponding to low 'slud ging tendency.

The following Table I gives theresults obtained in such determination on a Middle East crude oil.

Table I Vol. percent The tests in the upper half of the table at l520 intervals indicate that minimum sludge deposition occurs after heating to a temperature in the region of F. The further tests at 5 intervals around this figure show that the optimum elevated temperature is about F. and that considerable reduction in the sludge forming tendency of the oil occurs if it is heated to a temperature in the range l40150 F. In this case the upper temperature limit appears to be critical since if the heat treatment temperature is increased to F. practically no reduction in the sludge forming tendency occurs at all.

The following Table II gives the results of determinations of optimum heat treatment temperature for minimum sludge for various Middle Eastern crude oils. The temperature of the reservoir from which each oil came is also given.

It seems that the optimum heat treatment temperature is related to the reservoir temperature as shown in Figure 2 of the accompanying drawings,

The volume of sludge deposited in a given time depends on the amount of waxy material suspended in the crude oil and the rate at which that material settles. Heat treatment reduces the amount of waxy material available for deposition, but it is further beneficial in that it also reduces the settling rate of any remaining material. Examples of this are illustrated in Figure 3 (a, b, c and d) of the accompanying drawings. Crude oil samples were heated in a pressure tight bomb to 212 F. to remove their thermal history, cooled to 60 F. and then heated to the optimum temperature for minimum sludge or to an intermediate temperature of 95 F. These samples were allowed to stand at 60 F. in columns 3 feet high for various periods and the amount of material deposited was determined. Figures 3(a) and 3(b) show the deposition calculated as a percentage of the amount of waxy material present in the treated sample; this illustrates the reduction in settling rate. Figures 3(0) and 3(d) take into account the reductions in both the settling rate and amount of waxy material, and the deposition is calculated as a percentage of the total volume of the sample.

Figure 4 of the accompanying drawings illustrate by way of example how the process can be operated continuously on oil coming directly from a well.

The oil is first of all passed through a separator or stabilizer unit A and then through a cooler B where its temperature is reduced to 60-70 F. It is then warmed in 4 heat exchanger C and heated in heater D to the optimum temperature for minimum sludge forming tendency as previously determined for the oil from the field in question. The heated oil is finally cooled by heat exchange with the cold oil passing through heat exhanger C and passed to storage.

We claim:

1. A process for treating crude oil so as to reduce its tendency to deposit wax-containing sludge on storage, comprising heat treating a number of crude oil samples taken from a given batch of the crude oil to be treated, each sample being individually below about 100 F., by heating each sample to a progressively higher temperature from about 5-20 F. difierential for each sample and in the overall range from about 2l2 F., cooling each of the heated samples individually to below the lowest temperature value employed in heating the samples, allowing each of the samples to stand for a period of time suflicient to permit normal settlement of any material therein, and subjecting each sample to a vigorous settling force for a period of time sufi'icient to deposit the sludge that may be present therein thereby enabling the determination of the temperature value of one sample at which the minimum amount of sludge deposition for the particular batch of crude oil occurs, cooling the crude oil to be stored to a temperature below about F., and subsequently heating the crude oil to a temperature which is substantially the temperature of the sample having the minimum amount of sludge deposition, said temperature not being in excess of about F.

2. A process for treating crude oil as set forth in claim 1 wherein the crude oil is heated from a temperature below approximately 70 F. .to said treating temperatures.

3. A process for treating crude oil as set forth in claim 1 wherein the crude oil is first pre-cooled to a temperature not higher than approximately 70 F. and the pre-cooled oil then heated to said treating temperature.

References Cited in the file of this patent UNITED STATES PATENTS 64,855 Finn May 21, 1867 1,953,353 Lazar et al. Apr. 3, 1934 1,957,954 Haeck May 8, 1934 2,249,884 Carney July 22, 1941 2,315,935 Child Apr. 6, 1943 2,365,256 Edvarsson Dec. 19, 1944 2,572,425 Andersson Oct. 23, 1951 uNrrEn STATES PATENT OFFICE QE'llEl CAE I? CQRBECTION Patent Nos 2951 037 I August so, 1960 James lO 'Donnell et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patentshould read as corrected 'belowe Column l, line 32 for "or, better, still," read or, better still, column 2 line 6, for "schematially" read schematically line 9, for "advantage" read advantages line 38, for "narrow" read narrower column 3, line 43 for "illustrate" read illustrates column 4, line 5, for exhangefl read exchanger line $3 for "temperatures" read temperature Signed and sealed this 10th day of October 1961.

(SEAL).

Attest: ERNEST W. SWIDER v DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC 

1. A PROCESS FOR TREATING CRUDE OIL SO AS TO REDUCE ITS TENDENCY TO DEPOSIT WAX-CONTAINING SLUDGE ON STORAGE, COMPRISING HEAT TREATING A NUMBER OF CRUDE OIL SAMPLES TAKEN FROM A GIVEN BATCH OF THE CRUDE OIL TO BE TREATED, EACH SAMPLE BEING INDIVIDUALLY BELOW ABOUT 100*F., BY HEATING EACH SAMPLE TO A PROGRESSIVELY HIGHER TEMPERATURE FROM ABOUT 5-20*F. DIFFERENTIAL FOR EACH SAMPLE AND IN THE OVERALL RANGE OF 60-212*F., COOLING EACH OF THE HEATED SAMPLES INDIVIDUALLY TO BELOW THE LOWEST TEMPERATURE VALUE EMPLOYED IN HEATING THE SAMPLES, ALLOWING EACH OF THE SAMPLES TO STAND FOR A PERIOD OF TIME SUFFICIENT TO PERMIT NORMAL SETTLEMENT OF ANY MATERIAL THEREIN, AND SUBJECTING EACH SAMPLE TO A VIGOROUS SETTLING FORCE FOR A PERIOD OF TIME SUFFICIENT TO DEPOSIT THE SLUDGE THAT MAY BE PRESENT THEREIN THEREBY ENABLING THE DETERMINATION OF THE TEMPERATURE VALUE OF ONE SAMPLE AT WHICH THE MINIMUM AMOUNT OF SLUDGED DEPOSITION FOR THE PARTICULAR BATCH OF CRUDE OIL OCCURS, COOLING THE CRUDE OIL TO BE STORED TO A TEMPERATURE BELOW ABOUT 100*F., AND SUBSEQUENTLY HEATING THE CRUDE OIL TO A TEMPERATURE WHICH IS SUBSTANTIALLY THE TEMPERATURE OF THE SAMPLE HAVING THE MINIMUM AMOUNT OF SLUDGE DEPOSITION, SAID TEMPERATURE NOT BEING IN EXCESS OF ABOUT 170*F. 